The invention concerns a laser assembly arrangement, preferably a laser machine tool, with at least one optic element, for example at least one output and/or at least one focusing lens, which is arranged in the path of the laser beam and is at least partially permeable to the laser beam.
Laser arrangements of the type described have already been in use for a long time. The optic element or elements are functionally necessary for the laser arrangement.
Various types of monitoring and control devices are used on known laser tooling machines to guarantee high-quality machining results. For example, DE-A-37 10 816, DE-A-196 30 437 and an article by Haferkamp et al. in the journal VDI-Z No. 6, 1998, pp. 76 et seq. (Springer-VDI-Verlag GmbH and Co. KG, Duesseldorf, Germany) disclose devices connected to machine control for monitoring the place being machined on the workpiece in question. The place being machined is monitored through the focusing lens on the tooling head of the machine. The laser machine tool is controlled depending on the results of the observation. The devices already known use the known principle that the beam reflected or emitted by the workpiece at the machining point makes it possible to determine information about the machining process, and especially about the machining results.
This invention is devoted to solving a problem that is different from this.
In practice it is known that optic elements in laser assemblies, especially focusing lenses of laser tooling machines, become dirty in the course of operation due to deposits, like plasma coming from the machining point of the laser beam. As a result of the dirt, the optic element in question absorbs some of the laser beam passing therethrough. This leads to heating of the optic element which can cause evaporation of the material of the lens, especially in today""s high-powered lasers.
The goal of this invention is to remedy this problem.
The present invention solves this problem by providing at least one device for detecting the temperature of at least one of the optic elements of a laser assembly of the type mentioned at the beginning. It includes a component for detecting the intensity of the light emitted by the optic element in question so that the laser beam can be controlled in a way that affects the temperature of the optic element in question depending upon the light intensity detected. As soon as the temperature detected for the optic element being monitored reaches a value close to its evaporation temperature and a corresponding light intensity is detected, the laser beam is controlled in such a way as to preclude any further heating of the optic element. Control of the laser beam can consist, for example, of deflecting or reducing the energy of the beam and/or in turning the laser beam off. Reference to controlling the power of the laser beam as used herein includes both reducing the power of the beam and terminating the beam. Depending on the corresponding control, the optic element in question can be exchanged for a fully functioning optic element.
The use of the intensity of the light emitted by the optic element in question as a parameter for the temperature being detected or monitored has the advantage that the device used for temperature detection or monitoring can be arranged at a distance from the optic element, outside the path of the laser beam and thus in a variable spatial arrangement. Special devices for connecting the optic element to the detection or monitoring device, in the form of separate connecting lines, are not necessarily needed.
In addition, the light detected can be adjusted with a lower expenditure of interfering radiation than any invisible heat radiation produced such as that generated in machining the workpiece. This type of interfering radiation occurs, for example, with light that comes not from the optic element being monitored, but rather from its environment, but which nevertheless spreads out in the direction of the device for detecting the intensity of the light beamed by the optic element being observed.
Different technical solutions are conceivable according to the invention to detect the intensity of the light beamed by the optic element in question. The use of a camera would be possible, for example; according to the invention, a device that has at least one photosensitive sensor is preferred. A fiber optic cable can be used to monitor the optic element and a camera or a photosensitive sensor can be provided at the end of the cable.
In the interest of the optimal functionality and maximum operating safety of the device for monitoring the optic element or elements in question and thus in the interest of optimum functionality and maximum operating safety of the whole laser arrangement, the improvement in the invention provides that the device for detecting the intensity of the light emitted by the optic element in question, if necessary specifically at least one sensor, be connected to the optic element in question by at least one piece of equipment which enables separation of interfering electromagnetic radiation, especially process light from the light beamed or emitted by the optic element in question. This equipment allows the light beamed by the optic element to pass to the device for detecting the intensity of that light, if need be specifically to at least one sensor, and it stops electromagnetic interfering radiation, especially process light from the light beamed or emitted by the device for detecting the intensity of the optic element in question, if need be specifically from at least one sensor. This procedure ensures that electromagnetic radiation reaches the device for detecting the intensity of the light beamed by the optic element in question, whose intensity directly, but in any case after processing conducted about at a reasonable expense, permits a safe conclusion as to whether the temperature of the optic element being monitored has reached a critical value or will shortly.
In the case of laser assemblies whose laser beam is used as a machining tool, intensive electromagnetic interfering radiation is emitted from the machining point of the laser beam in the form of interfering light radiation. By means of the procedure in the invention described above, the influence of this interfering light radiation is at least kept small during the detection of the intensity of the light beamed by the optic element being monitored.
The invention provide, as a device for separating the electromagnetic interfering radiation, especially process light, and light emitted by the optic element in question, an advantageous improvement at least shielding the device for detecting the intensity of the light emitted by the optic element in question, if need be especially at least one sensor.
According to the invention, the preferred type of shielding is at least one optic filter arranged between the device for detecting the intensity of the light emitted by the optic element in question, if need be especially at least one sensor, and the optic element being monitored. This type of filter is wavelength-related shielding, i.e., shielding by means of which electromagnetic radiation of a certain wavelength or a certain wavelength range can be stopped by the device for detecting the intensity of the light beamed by the optic element in question.
Since light emitted by output or focusing lenses normally has a wavelength that is above 600 nm in magnitude, it may be useful to provide at least one optic filter that is permeable to light with a wavelength that is above 600 nm in magnitude and is impermeable to electromagnetic radiation with a wavelength that is under 600 nm in magnitude.
Those features of the laser arrangement in the invention that are given in the characterizing parts of various claims are used as effective shielding associated with low structural expense, on the device for detecting the intensity of the light emitted by the optic element in question. The claims describe shielding whose effectiveness is based on the arrangement of the device for detecting the intensity of the light emitted by the optic element in question compared to the optic element being monitored and the monitoring channel according to the claims.
Another preferred embodiment of the invention provides that the sensor or at least one of the sensors for detecting the intensity of the light emitted by optic element in question is a diode. These types of diodes are proven, functionally safe components that can be integrated simply into a machine""s controls.
Automation of the overheating protection of the optic elements of the laser assembly of the invention is used so that xe2x80x94as in the case of another variation of the invention that is providedxe2x80x94the device for detecting the intensity of the light beamed or emitted by the optic element in question is connected to the machine controls through an evaluation device. The evaluation device has a comparison unit by means of which an actual value assigned to the light intensity detected can be compared with a predetermined reference value. The laser beam can be controlled, depending on the results of the comparison, by means of the controls in a way that affects the temperature of the optic element in question.
The invention""s preferred method for controlling the laser beam to protect the optic element in question from overheating consists of shutting off the laser beam. For this purpose, the invention provides that the controls be connected to the laser generator and the latter can be shut off or reduced in power by means of the controls.
The laser assembly in the invention is adjusted to changing requirements in individual cases so that the reference value is variable. Variability of the reference value makes sense since different optic elements may also have different evaporation temperatures, for example.
In the case of the embodiments of the laser arrangement in the invention with sensors in the form of diodes, an actual value assigned to the diode current and/or the diode voltage as the light intensity detected can be compared to a corresponding reference value by means of the comparison unit in the evaluation device.
To prevent malfunctions of the device and protect the optic element in question from overheating, the invention also provides for the evaluation device to have a correction unit, by means of which an actual output value assigned to the light intensity detected can be corrected for interfering influences and the actual adjusted value can be compared with the reference value in question by means of the comparison unit. This basic approach to the solution is translated into the laser assembly in the invention with sensors in the form of diodes. Highly functionally safe overheating protection of the optic element in question is guaranteed when a correction unit according to the claims is provided in combination with one or more of the above-mentioned devices for separating electromagnetic interfering radiation and light emitted by the optic element in question.
The connection between the evaluation device and the control is produced in one preferred embodiment of the invention by a threshold switch, by which the control can be effected by controlling the laser beam, as soon as the actual value assigned to the light intensity detected, if necessary the corrected actual value, exceeds the reference value.
To be able to prevent faulty control of the laser beam, one preferred form of embodiment of the laser arrangement or laser tooling machine in the invention provides that the device for detecting the intensity of the light emitted by the optic element in question and/or the evaluation device can be turned on or off, especially depending on the operating status of the laser assembly or laser machine tool. The possibility of turning off the device for detecting light intensity and/or the evaluation device can be used meaningfully on a laser tooling machine at the time when the laser beam is xe2x80x9cplungedxe2x80x9d into the workpiece to be machined. This plunging of the laser beam is associated with a jerking evolution of light that could be assigned to the optic element being monitored by the evaluation device of the laser arrangement and would then lead to unfounded control of the laser beam, especially shut down.
In the interest of the greatest possible automation of the operation of the laser arrangement in the invention, the device for detecting the intensity of the light emitted by the optic element in question and/or the evaluation unit and/or the controls are computer-aided.
In one preferred embodiment of the invention, a CO2 laser generator is provided as the laser generator. The laser beam produced by this type of gas laser is not visible and cannot be detected by a photo diode, for example.